Attaching components to a printed circuit card

ABSTRACT

Coupling components to an underlying substrate using a composition of a polymer and magnetic material particles. Upon applying the composition between the component and the printed circuit board, the composition may be subjected to a magnetic field to align the magnetic material particles into a conductive path between the component and the underlying substrate. At the same time the polymer-based material may be cured or otherwise solidified to affix the conductive path formed by the magnetic material particles.

BACKGROUND

The present invention relates to circuit components and, in particular,to attaching components to underlying substrates.

BACKGROUND OF THE RELATED ART

There may be several techniques for attaching components, such as anintegrated circuit, to underlying substrates, such as printed circuitcards. However, these techniques may have multiple problems. Forexample, eutectic lead solder may be used to attach a component to anunderlying substrate because the eutectic lead solder has a low meltingtemperature and good viscosity, but environmental regulations may forcelead solders to be phased out of manufacturing. Other solders that donot contain lead, including, but not limited to, tin alloys, may be usedto connect components to underlying substrates. However, these soldershave high melting temperatures that may damage the components orunderlying substrates during the process of attaching them together.Other methods of attaching components and underlying substrates, such ascup and cone suspension, may have contact resistance problems betweenthe surfaces of the component and the underlying substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 shows an embodiment of the invention having an underlyingsubstrate coupled to a component by a solidified bi-materialcomposition;

FIG. 2 shows an embodiment of the invention having an underlyingsubstrate and screen pads;

FIG. 3 shows an embodiment of the invention having an underlyingsubstrate, a component, and a non-solid bi-material composition;

FIG. 4 shows an embodiment of the invention in the form of an underlyingsubstrate, a component, and a bi-material composition in the presence ofa magnetic field and ultraviolet light;

FIG. 5 shows an embodiment of the invention having an underlyingsubstrate coupled to a component by a solidified bi-materialcomposition; and

FIG. 6 shows an embodiment of the invention in the form of a flowchartof a method for forming the conductive path between the component andthe underlying substrate.

DETAILED DESCRIPTION

The following description makes reference to numerous specific detailsin order to provide a thorough understanding of the present invention,however, it is to be noted that not every specific detail need beemployed to practice the present invention. Additionally, well knowndetails, such as particular materials or methods have not been describedin order to avoid obscuring the present invention.

Referring to FIG. 1, an embodiment of the invention is shown in the formof an underlying substrate 101 coupled to a component 111 by aconductive solidified bi-material composition 113 and 115. Thebi-material composition 113 and 115 may first be subjected to a magneticfield in order to align the magnetic material particles 121 into aconductive path. The composition 113 and 115 may then be solidified inorder to fix the conductive paths of the magnetic material particles121. The magnetic material particles 121 may form a conductive paththrough the polymer-based material 117 and 119 from the component 111 tothe screen pads 103 and 105 coupled to the underlying substrate 101. Thescreen pads 103 and 105 may be coated with pre-coating layers 107 and109.

Referring to FIG. 2, an embodiment of the invention is shown in the formof an underlying substrate 101 and screen pads 103 and 105 pre-coatedwith a conductive composition. The underlying substrate 101 may be asubstrate such as, but not limited to, a printed circuit card, analuminum lead frame, and a fine-pitched ball grid array. A component(not shown) such as, but not limited to, an integrated circuit, may becoupled to the underlying substrate 101 through screen pads 103 and 105and a bi-material composition (not shown). The screen pads 103 and 105,shown in FIG. 2, may be electrically coupled to the underlying substrate101. A conductive composition may be used to pre-coat the screen pads103 and 105 before coupling the component to the underlying substrate101. In this illustrated embodiment, the conductive composition used topre-coat the screen pads 103 and 105 is the same bi-material compositionused to establish a conductive path between the component and theunderlying substrate 101. Pre-coating layers 107 and 109 may make thesurface of the screen pads 103 and 105 more adherable for laterdeposition of the bi-material composition. If the bi-materialcomposition is used for pre-coating layers 107 and 109, it may not becured or solidified before coupling the component to the underlyingsubstrate 101. While the pre-coating layers 107 and 109 are shown inFIG. 2, in order to perform the invention, the pre-coating layers 107and 109 may be omitted in some embodiments.

In one embodiment of the invention, the bi-material composition may beformed by mixing a polymer-based material with magnetic materialparticles. The polymer-based material may be a polymer, including, butnot limited to, conductive polymers, thermoplastic polymers, andthermoset polymers. Some specific polymer-based materials that may beused include, but are not limited to, polyamide, ultraviolet lightcurable epoxies, and photo-resist polymers. In one embodiment, apolymer-based material, such as but not limited to photo-resist, mayhave approximately the same coefficient of thermal expansion as theunderlying substrate 101. Having approximately the same coefficient ofthermal expansion may increase the reliability of the interface betweenthe polymer-based material of the bi-material composition and theunderlying substrate 101. Otherwise, the greater the difference betweenthe coefficients of thermal expansion between polymer-based material andthe underlying substrate 101, the greater the difference of contractionor expansion between the two during temperature changes andcorrespondingly, more fatigue may be experienced at the interfacebetween polymer-based material and the underlying substrate 101.

The magnetic material particle may be a material, including, but notlimited to, ferro-magnetic metal, magnetic ceramics, and ferro-electricmaterials. Materials that may be used, include, but are not limited to,iron, barium strontium titanate, strontium tantalum oxide, andperoskovites. In addition, magnetic material particles may be made outof magnetite or metallic materials with low magnetic retentivity.Magnetic material particles may be small in size and acicular shaped(i.e. with a high aspect ratio morphology). In one embodiment, theapproximate dimensions of a magnetic material particle may be one micronby two microns by ten microns. However, other dimensions may also bewithin the scope of the invention.

Several by-weight ratios of the polymer-based material and magneticmaterial particles in the bi-material composition are within the scopeof the invention. For example, in one embodiment, the polymer-basedmaterial may constitute approximately 40% by weight of the bi-materialcomposition, while the magnetic material particles may constituteapproximately 60% by weight. Other by-weight percentages may be used,depending on several factors, including, but not limited to, the type ofpolymer-based material, the type of magnetic material particles used,and the size of the magnetic material particles used.

Magnetic material particles may need to be mixed uniformly into thepolymer-based material. Therefore, if the polymer is a thermoplastic,the polymer may be in liquid form when mixed with the magnetic materialparticles, and if the polymer is a thermoset polymer, the polymer may bein a soft, or liquid, uncured form when mixed with the magnetic materialparticles. After forming the bi-material composition by mixing thepolymer-based material and the magnetic material particles together, thebi-material composition may be put through a screen onto the screenpads. The screen may act as a stencil to control the volume andplacement of the bi-material composition onto the underlying substrate101. To put the bi-material composition through the screen, the holes inthe screen may be lined up with the areas or components where thebi-material composition is to be deposited, and a squeegee may be usedto push it through the screen in a screen printing process. The screenmay allow the location and amount of bi-material composition beingdeposited to be controlled. Other methods of putting the bi-materialcomposition through the screen, including, but not limited to, pullingthe bi-material composition through the screen with a magnet or vacuum,may also be within the scope of the invention. Other methods ofdepositing the bi-material composition into a pre-coating layer 107 and109 on the screen pads 103 and 105 may also be within the scope of theinvention. For example, in one embodiment, the bi-material compositionmay be deposited directly without the use of a screen.

Referring to FIG. 3, an embodiment of the invention is shown in the formof an underlying substrate 101, a component 111, and a non-solidbi-material composition 113 and 115. The underlying substrate 101 may becoupled to screen pads 103 and 105. The bi-material composition 113 and115 may be used to form a pre-coating layer 107 and 109 on the screenpads 103 and 105. The bi-material composition 113 and 115 may bedeposited on the screen pads 103 and 105 before the component 111 isplaced on the underlying substrate 101. In another embodiment of theinvention, the component 111 may be placed onto the screen pads 103 and105 before the bi-material composition 113 and 115 is deposited. Inaddition, while the bi-material composition 113 and 115 is shown on theside and on top of the component 111 in the illustrated embodiment ofFIG. 3, in another embodiment, the bi-material composition 113 and 115may be confined to the sides or confined to the sides and bottom of thecomponent 111. When first deposited, the bi-material composition 113 and115 may be in a liquid state with magnetic material particles 121 inrandom arrangement in the polymer-based material 117 and 119.

Referring to FIG. 4, an embodiment of the invention is shown in the formof a underlying substrate 101, a component 111, and a bi-materialcomposition 113 and 115 being exposed to a magnetic field and UV light.In the embodiment shown in FIG. 4, an underlying substrate 101 may becoupled to a component 111 through screen pads 103 and 105 by abi-material composition 113 and 115 with magnetic material particles121. Upon application of the magnetic field, which may be provided bymagnets 403 and 405, the magnetic material particles 121 may group andalign with each other to form a magnetic material particle path. Themagnetic material particles 121 in the bi-material composition 113 and115 may be acicular in shape. The magnetic material particles 121 may belong, thin, and flat to increase the number of surface contact pointsthat may improve the conductive path formation.

The magnetic field strength used may be less than a level that may causesensitive devices on or near the underlying substrate 101 to be affectedby soft errors. For example, while a weaker magnetic field may be needednear central processing units, a stronger magnetic field may be used forpassive components such as capacitors and resistors. While magnets 403and 405 are shown to supply the magnetic field, other sources ofmagnetic fields including, but not limited to natural magnets andelectro-magnets, may also be within the scope of the invention.

A secondary magnetic attraction from metallic surfaces on the component111 may bend the magnetic material particle path enough to form aconductive path between component 111 and screen pads 103 and 105. Inthe context of the invention, ‘bend’ means that the lines of magneticflux are affected by the secondary magnetic attraction from metallicsurfaces, so that the magnetic material particle path is directed to themetallic surfaces of component 111.

While the magnetic field is being applied, a UV light from a UV lightsource, such as UV light sources 401 and 407, may be applied to thebi-material composition 113 and 115. While the UV light 401 and 407cures the bi-material composition 113 and 115, causing it to stiffen,the magnetic material particles 121, under the influence of the magneticfield, may form conductive paths and eventually be trapped in thesolidified polymer-based material in conductive pathways between thecomponent 111 and the screen pads 103 and 105.

While UV lights 401 and 407 are shown in the embodiment of theinvention, other lights such as, but not limited to, regular light andinfrared light, may also be used to cure the polymer-based material 117and 119 in the bi-material composition 113 and 115. Heat sources mayalso be used to cure the polymer-based material 117 and 119 byincreasing the polymer-based material's temperature. In addition tousing lights 401 and 407 or heat sources, the polymer-based material 117and 119 may also be cured by using a curing agent mixed into thebi-material composition 113 and 115 at the time the magnetic field isapplied. Other methods of curing the polymer-based material 117 and 119may also be within the scope of the invention. In other embodiments ofthe invention, the polymer-based material 117 and 119 may be athermoplastic polymer. For thermoplastic polymers, instead of applyingUV lights 401 and 407 or a curing agent, a heat source may used toliquefy the polymer-based material 117 and 119 and then the heat sourcemay be removed. In another embodiment of the invention, thethermoplastic polymer may be solidified by lowering its temperature.

Several factors may also affect the formation of conductive pathsbetween the component 111 and the screen pads 103 and 105. For example,the viscosity of the polymer-based material 117 and 119, the density ofthe magnetic material particles 121, the shape of the magnetic materialparticles 121, the distribution of the magnetic material particles 121,the concentration of the magnetic material particles 121 in thebi-material composition 113 and 115, and the temperature conditionsduring the application of the magnetic field may affect the speed atwhich the magnetic material particles 121 align and form a conductivepath between the component 111 and the underlying substrate 101.

For example, if the viscosity of the bi-material composition 113 and 115is too high, the magnetic material particles 121 may not be able to moveinto alignment before the polymer-based material 117 and 119 solidifies.However, if the viscosity of the bi-material composition 113 and 115 istoo low, the magnetic material particles 121 may move quickly intoposition and then slightly disjoin in a random alignment according tothe magnetic field. The higher the viscosity of the polymer-basedmaterial 117 and 119, the higher the attraction force may be betweenclose adjacent magnetic material particles 121. However, with a lowviscosity polymer-based material 117 and 119, the magnetic materialparticles 121 may be more influenced by the magnetic force of themagnets 403 and 405 than the attraction force between them and may beslightly pulled away from each other to align with the magnetic field.In a high viscosity polymer-based material 117 and 119, the magneticmaterial particles 121 may have a stronger attraction at close rangethan the magnetic force pulling them into alignment. The viscosity ofthe bi-material composition 113 and 115 may need to be adjusted to allowthe attraction between each magnetic material particle 121 to influencethe magnetic material particles 121 into forming a path and bendingbetween the component 111 and the screen pads 103 and 105. Similarproblems may occur if the shapes of the magnetic material particles 121are too big or too small or if their density and concentration is toogreat or too small.

Referring to FIG. 5, an embodiment of the invention is shown in the formof an underlying substrate 101 coupled to a component 111 by aconductive solidified bi-material composition 113 and 115. In theembodiment shown in FIG. 5, the bi-material composition 113 and 115 maybe subjected to a magnetic field in order to align the magnetic materialparticles 121 into a conductive path. Then the composition 113 and 115may be solidified in order to fix the conductive paths of the magneticmaterial particles 121. The magnetic material particles 121 may form aconductive path through the polymer-based material 117 and 119 from thecomponent 111 to the screen pads 103 and 105 coupled to the underlyingsubstrate 101.

While one component 111 is shown in the embodiment in FIG. 5, multiplecomponents may be coupled to the underlying substrate 101 using theinvention. Components 111 may be applied at the same time, or thecomponents 111 may be applied one at a time. In another embodiment ofthe invention, the components 111 may be applied in shifts, by which aselected type of component 111 is applied to the underlying substrate101 in each shift. While setting the bi-material composition 113 and 115on the selected type of components 111, a magnetic field with a strengthsufficient for the specific amount and type of bi-material composition113 and 115 used with the selected components 111 may be applied atapproximately the same time the polymer-based material 117 and 119 issolidified. For example, bigger components 111 may require morebi-material composition 113 and 115 to form the appropriate conductiveconnections, and with bigger components 111, there may be morebi-material composition 113 and 115 to solidify and more magneticmaterial particles 121 to align. The magnetic field strength and methodof solidifying the polymer-based material 117 and 119 may need to beadjusted for the components 111 using a greater amount of bi-materialcomposition 113 and 115. After the conductive connections are formed inthe bi-material composition 113 and 115, the component connection to theunderlying substrate 101 may be electrically tested.

Referring to FIG. 6, a flowchart of a method of an embodiment of theinvention is shown for electrically coupling a first component to asecond component. At block 601, a bi-material composition of magneticmaterial particles and a polymer-based material may be mixed. At block603, the bi-material composition may be put through a screen. At block605, a first component, such as, but not limited to, an underlyingsubstrate, may be pre-coated with a layer of conductive composition. Atblock 607, the bi-material composition may be deposited on a firstcomponent. At block 609, a second component may be placed onto a firstcomponent at the site where the bi-material composition is deposited. Atblock 611, a magnetic field may be applied to the bi-materialcomposition to form an aligned path of the magnetic particles and bendsaid aligned path of magnetic material particles to form part of aconductive path between the first component and the second component. Atblock 613, the polymer-based material may be solidified. For example, acuring compound or UV light source may be applied if the polymer-basedmaterial is a thermoset polymer. At block 615, after the polymer-basedmaterial has been solidified and the magnetic material particles havebeen fixed in the bi-material composition, the conductive path formed bythe magnetic material particles between the first component and thesecond component may be tested.

Although an exemplary embodiment of the invention has been shown anddescribed in the form of a method for attaching components to anunderlying substrate, many changes, modifications, and substitutions maybe made without departing from the spirit and scope of the claimedinvention.

We claim:
 1. An apparatus comprising: a polymer-based material; and aplurality of magnetically aligned magnetic material particles in saidpolymer-based material to form an electrically conductive path through apart of said polymer-based material, wherein the dimensions of the saidmagnetic material particles are approximately one micron by two micronsby ten microns.
 2. The apparatus of claim 1 wherein said polymer-basedmaterial is selected from a group consisting of conductive polymers,thermoplastic polymers, and thermoset polymers.
 3. The apparatus ofclaim 1 wherein said polymer-based material is a polyamide.
 4. Theapparatus of claim 1 wherein said polymer-based material is anultra-violet light curable epoxy.
 5. The apparatus of claim 1 whereinsaid magnetic material is selected from a group consisting offerro-magnetic metal, a magnetic ceramic, and a ferro-electric material.6. The apparatus of claim 1 wherein said apparatus is comprised ofapproximately 40 percent by weight polymer-based material andapproximately 60 percent by weight magnetic material particles.
 7. Theapparatus of claim 1 wherein said magnetic material particles areacicular shaped.
 8. The apparatus of claim 1 wherein said polymer-basedmaterial is a photo-resist material.
 9. The apparatus of claim 1 whereinsaid magnetic material particles form part of the electricallyconductive path from the integrated circuit to the underlying substrate.10. The apparatus of claim 1 wherein said magnetic material is selectedfrom a group consisting of iron, barium strontium titanate, strontiumtantalum oxide, and perovskites.
 11. An apparatus comprising: apolymer-based material; and a plurality of magnetically aligned,magnetic material particles in said polymer-based material to form anelectrically conductive path through a part of said polymer-basedmaterial, wherein the said magnetic material is selected from a groupconsisting of barium strontium titanate, strontium titanium oxide andperovskites.
 12. The apparatus of claim 11 wherein said polymer-basedmaterial has a first coefficient of thermal expansion and interconnectsan integrated circuit and an underlying substrate having a secondcoefficient being approximately the same as the first coefficient ofthermal expansion.
 13. The apparatus of claim 12 wherein said magneticparticles form part of the electrically conductive path from theintegrated circuit to the underlying substrate.